1. Field of the Invention
The present invention relates to the preparation of electrolytes for batteries, and more particularly, relates to the preparation of non-aqueous liquid polymer host network electrolytes for batteries.
2. State of the Art
In recent years workers in the battery art have begun to understand the advantages of manufacturing batteries that have polymer electrolytes and sheet-like cathodes and anodes. The advantages include lower battery weights than batteries that employ liquid electrolytes, longer service life, relatively high power densities, relatively high specific energies, and elimination of the danger of acid spillage.
Batteries of the type having polymer electrolytes and sheet like cathodes and anodes are generally formed of laminated sheets comprising thin layers of a cathode, an electrolyte, and an anode, which may be adapted into different configurations for various applications. The anode in such batteries is preferably lithium. Because lithium is highly reactive, its use as a sheet-like layer in contact with the electrolyte requires that the battery construction, and the electrolyte in particular, be free of contaminates, especially water.
The polymer is initially formed in a liquid state, and is later polymerized and formed into a solid sheet which is then incorporated into the battery. Removal of water from the electrolyte is best accomplished while the electrolyte is in liquid state, before the water becomes entrapped in the solid form and while the water is still substantially free to be removed. An electrolyte of this type is described in U.S. Pat. No. 4,925,751 to Shackle et al.
Most conventional methods for removing water from non-aqueous liquids involve passing the liquid through a column packed with a suitable desiccant agent. As the liquid flows through the column, it contacts the desiccant agent, which is selected to have a high affinity for water over the other components of the liquid. The water in the liquid which contacts the desiccant agent is thereby removed. One example of an apparatus for such a method is a column packed with a molecular sieve material.
This method of removing water from a non-aqueous liquid by contact with a desiccant agent has several disadvantages, however. The liquid may become contaminated by particulate matter or soluble material present in the desiccant agent. The desiccant may have some affinity for the liquid, or some component of the liquid, which may cause some of the material to be lost in the desiccant column. Furthermore, material other than water trapped in the desiccant makes drying and cleaning of the desiccant for reuse difficult. In addition, if the liquid contains hazardous materials, disposal of contaminated desiccant may require special handling and entail extra costs for disposal.